Developing device, and image forming apparatus and process cartridge using the developing device

Abstract

A developing device including a rotating developing roller bearing toner thereon, capable of developing an electrostatic latent image with the toner; a toner layer forming member configured to form a toner layer on the developing roller, and charge the toner of the toner layer at a nip between the developing roller and the toner layer forming member; and a toner supplying device configured to supply fresh toner to the developing device, wherein a charge quantity (q) of the toner on the developing roller varies according to the following equation q(t)=A·{1−exp(−t/t g )} wherein t represents a nip passing time of the toner on the developing roller, t g represents a time constant of charging the toner, and A represents a constant, and wherein the time constant t g is smaller than a rotation time of the developing roller per rotation; and an image forming apparatus and a process cartridge using the developing device.

1. A developing device for developing an electrostatic latent image formed on an image bearing member, comprising:
 a rotating developing roller bearing toner thereon, capable of developing the electrostatic latent image with the toner; 
 a toner layer forming member configured to form a toner layer on the developing roller, and charge the toner of the toner layer at a nip between the developing roller and the toner layer forming member; and 
 a toner supplying device configured to supply fresh toner to the developing device, 
 wherein a charge quantity (q) of the toner on the developing roller varies according to the following equation:
     q ( t )= A·{ 1−exp(− t/t   g )}  (1) 
 
  wherein t represents a nip passing time of the toner on the developing roller, t g  represents a time constant of charging the toner, and A represents a constant, 
 and wherein the time constant t g  is smaller than a rotation time of the developing roller per rotation. 
 
   
   
     2. The developing device according to  claim 1 , wherein the time constant t g  of the toner on the developing roller is less than 4 times t g  of the supplied fresh toner. 
   
   
     3. The developing device according to  claim 1 , wherein the toner has an average circularity of from 0.96 to 1.00. 
   
   
     4. The developing device according to  claim 1 , wherein the toner has a volume average particle diameter of from 4 to 10 μm, and comprises an external additive having a volume average particle diameter of from 50 to 150 nm. 
   
   
     5. The developing device according to  claim 1 , further comprising a toner removing device configured to remove not less than 80% of the toner remaining on the developing roller after the toner passes the nip. 
   
   
     6. The developing device according to  claim 1 , further comprising:
 an agitator configured to agitate the fresh toner supplied by the toner supplying device; and 
 a feeding roller configured to feed the toner from the agitator to the developing roller, 
 wherein the feeding roller rotates in the same direction as the developing roller. 
 
   
   
     7. An image forming apparatus comprising:
 an image bearing member configured to bear an electrostatic latent image; 
 an electrostatic image forming device configured to form the electrostatic latent image on the image bearing member; and 
 a developing device configured to develop the electrostatic latent image with a toner to form a visible image on the image bearing member, 
 wherein the developing device is the developing device according to  claim 1 . 
 
   
   
     8. A process cartridge comprising:
 an image bearing member configured to bear an electrostatic latent image; and 
 the developing device according to  claim 1 . 
 
   
   
     9. A method for developing an electrostatic latent image, comprising:
 charging an image bearing member; 
 forming an electrostatic latent image on the charged image bearing member; and 
 developing the electrostatic latent image with a toner to form a visible image on the image bearing member using the developing device according to  claim 1 .